The present invention relates to the high-volume treatment of waste water or other aqueous (or gaseous) environments with ultraviolet radiation for the destruction of toxic organic compounds, microbial species, and the like.
Various undesirable substances, such as heavy organic molecular compounds and microbial species, are often carried in waste water or other effluents, or in gaseous or other matrix environments, in which they may prove toxic in subsequent uses of the carrier material.
One known process for sterilizing or disinfecting the carriers of these compounds is through irradiation with ultraviolet (UV) radiation.
For treatment of waste water, for example, the water under treatment is mixed with ozone or peroxide and subsequently passed through a processing chamber where it is irradiated by a UV source typically in the form of one or more UV lamps as the water flows past. The most common form of lamp employed in such chambers has historically been the low-pressure linear mercury lamp. Recently much more powerful medium-pressure linear mercury lamps have been introduced. For the most part, however, these lamps have merely been used in place of the low-pressure lamps in processing chambers of conventional design intended for low-pressure lamps, and only limited attempts have been made to redesign the processing chamber to accommodate the medium-pressure lamps. Thus, known processing chamber designs for use with medium-pressure lamps share many characteristics--both positive and negative--in common with chambers for low-pressure lamps.
The conventional UV processing chambers are subject to a number of deficiencies and drawbacks. The commonly employed low-pressure mercury lamps have a low power output in the deep UV region. Their radiation is used to create free radicals by photolytic action with ozone or peroxide, which in turn destroys toxic substances. Because of the low power of such lamps, however, the water has to travel relatively slowly through the processing chamber so that the travel time of the water through the operative portion of the chamber is often comparable to the diffusion time for contaminants through the water. As a result, contaminants in the water may foul the UV lamps and produce significant screening of the UV radiation. To solve this problem in the past, special devices have been used to scrub the buildup from the lamps while the lamps are operating, or water was continually mixed by propellers in the chamber, or else it has been necessary to shut the system down periodically to permit the lamps to be cleaned.
To treat large volumes of water such as required in any industrial treatment facility, a matrix type array of such UV lamps is used, where each lamp of the array is immersed in the water under treatment. For large industrial systems as many as 200 low-pressure mercury lamps may be used. As a result, such systems tend to be bulky and may be so massive as to require a special concrete base to support the aggregate weight of the chamber and processed water, which can reach ten or more tons.
The trend in the water treatment industry is now to switch to medium-pressure lamps instead of low-pressure ones. The power of the medium-pressure lamps exceeds the power of low-pressure lamps by a factor of about 100 to 150. More specifically, the medium-pressure lamps have a typical power rating of 200 to 250 watts per inch of lamp length and may be as high as 300 watts per inch. This is to be compared with a maximum of two watts per inch found in low-pressure mercury lamps. Thus, the number of lamps in systems of comparable throughput is reduced significantly. The medium-pressure lamps, however, also generate significantly more heat (about 50 percent of their output). Hence, these lamps have to be cooled. The use of these lamps is not yet widespread. When medium-pressure lamps are used, however, they are usually also disposed in arrays in conventional chambers as are the low-pressure lamps. Such systems are desired for processing large volumes of water (100 gallons per minute or more). Alternatively, a design is sometimes used which is especially adapted for medium-pressure lamps and high-volume processing, in which a plurality of long medium-pressure lamps, up to seven feet in length, are each contained in a cylindrical chamber, and the power for each such module can attain about 15 kilowatts.
Although the use of medium-pressure mercury lamps eliminates some of the drawbacks of systems with low-pressure linear mercury lamps, such as their bulky size and excessive weight, other drawbacks of conventional UV treatment systems were merely carried over into systems with linear medium-pressure mercury lamps. Specifically, the medium-pressure lamp systems still employ unnecessarily complex matrix arrays for the lamp geometries and still require the whole system to be drained for replacement of each individual lamp.
In fact, with the arrays of either the low-pressure or medium-pressure lamps, when a lamp must be replaced or cleaned, the whole system must be shut down and drained. This occurs on a periodic basis because lamp lifetime is well known and premature burnout is statistically insignificant. At that time the system is drained and the lamps are individually replaced, which is a tedious and time-consuming procedure.
Thus, matrix arrays of lamps present two main drawbacks, notwithstanding their benefits. The fact remains that despite the known reliability of standard lamps, failures can occur due to such extraneous factors as improper cooling or electrical failure. In this case the action of the failed lamp in the array of lamps is not covered by the remaining lamps because in such systems the lamps are positioned to treat predetermined portions of the processing chamber. The UV radiation from the other lamps will not generally reach a particular portion of the chamber with sufficient intensity to substitute for a failed lamp. As a result, when a lamp fails, not all the water will be treated effectively if the system is permitted to continue operating. To guard against this, many systems have automatic controls which shut down the system when a failure in lamp performance is detected so as to prevent an outflow of untreated water.
Another drawback of the standard lamp array geometry is the non-uniform distribution of radiation intensity in the processing chamber, which results from the lamps' complicated overlapping circles of action needed to insure that even the farthest reaches of the volumes allocated to the individual lamps are subjected at least to the minimum operative UV levels. Such an arrangement undesirably produces "pockets" of excess UV exposure mostly within close distances to the lamps, which results in an overall waste of UV energy, which may be as high as 30 percent.
In some known systems the "pocket" effect is compensated somewhat by intensive mixing of the water under treatment so that portions of the water pass both through areas of higher and lower UV exposure, which enables one to decrease the UV intensities of the lamps (or to increase the throughput of treated water). Although the overall utilization of UV energy is improved in such case, in a chamber with complicated geometry and many lamps and in a chamber with a low speed of processed water through the chamber, the proper mixing of water is difficult to maintain throughout the chamber. Thus, this approach is not in widespread use, and usually the underutilization of UV in such systems is simply accepted.